Electromagnetic compatibility (EMC) testing is widely performed on equipments, such as complete systems, integrated circuits, printed circuit boards (PCBs) and other electronic modules, to determine whether the equipments do not radiate more radio frequency (RF) energy than either allowed by regulations or acceptable to avoid interference with wireless receivers, or to determine if the equipments are susceptible to electromagnetic (EM) disturbances. An EMC test may involve a number of different EM analyses. As an example, an EMC testing may involve radiating electromagnetic waves at the equipment, measuring the emissions from the equipment or testing the immunity to electrostatic discharges (ESD).
EMI testing is usually performed according to standards, e.g., FCC normally uses a semi-anechoic chamber or an open area test site to measure the fields in the far field region. This methodology does provide little insight into the root cause of EMI problems. Further, EMI analysis can be performed by near field scanning, i.e., measuring local electric or magnetic field around equipment under test (EUT) to identify areas of strong electric or magnetic field. This near field information may then assist in identifying the cause of an EMI problem of the EUT based on an implicit assumption that an area of strong field is the cause of the EMI problem. However, this implicit assumption is often incorrect for various EUTs.
An immunity or ESD analysis can be performed by subjecting the EUT to strong electromagnetic fields (immunity) or injecting ESD currents into the EUT at different locations and determining whether an error has occurred because of the RF field or ESD current stress injected into the selected location.
The difference between the immunity analysis and the ESD analysis is the type of noise injected. Modulated RF signals are usually injected for the immunity analysis, whereas narrow pulses (having one or sub nanosecond rise time) are injected for the ESD analysis. The other relevant difference is that immunity analysis subjects the EUT to fields, most often in the far field region of the transmitting antenna, while ESD testing injects currents directly into the EUT. Indirect ESD testing, which subjects the EUT only to the fields of the ESD, is also performed.
A method that provides better insight into the possible root cause of an immunity or susceptibility problem is susceptibility scanning. In this method, a probe is moved above the equipment (e.g., PCB, cables etc.) and a strong local field is caused by injecting pulses or RF signals into the probe. The probe is moved around and the reaction of the equipment is observed. This way, local areas of higher susceptibility can be identified.
The near field EMI scanning and the near field susceptibility scanning both identify local effects, which are difficult to connect to the system level performance of the EUT. Thus, strong local fields are not necessarily the cause of strong radiated emissions, and local areas of high susceptibility are not necessarily the reason for immunity or ESD problems as they show up if the complete system is tested in accordance to the standards, such as IEC 61000-4-3 (radiated immunity) or IEC 61000-4-2 (ESD).
Although the above analyses can provide EMC information about EUTs, there is a need for a system and method for EMC testing that helps to connect local effects with system effects.